I mean, it's also definitely possible that MAPSS could lead to an offer better (in terms of rank) than Penn. They give a list of funded PS Ph.D. offers their Class of 2012 received:
"Of the 18 candidates we supported in 2012, 16 (89%) have offers from: Chicago (4), Brown, North Carolina, Harvard, NYU, Yale, Texas, Georgetown, UC-Berkeley, George Washington, Johns Hopkins, Cornell, Toronto, Michigan, UC-Los Angeles, Washington-Seattle, Notre-Dame, Wisconsin, Minnesota, McGill, Indiana, Temple, Florida, SUNY-Binghamton, UC-Santa Cruz, UC-Santa Barbara, Southern California, York, Michigan State." http://mapss.uchicago.edu/the_ma/why_mapss/our_outcomes/phd_placements
Something like half of those programs are equally or lower ranked than Penn, and the rest higher. So yeah, I guess it might be a gamble but less so given that you have full funding!